The present invention relates generally to methods and apparatus for gravel packing a well, and, more specifically relates to methods and apparatus for gravel packing a well with only a single trip of the tool string into the wellbore, which method may also provide for the perforating of the well on such single trip.
Techniques are well known in the oil and gas industry for controlling sand migration into wells penetrating unconsolidated formations by gravel packing the wells. Such gravel packing typically consists of depositing a quantity, or "pack," of gravel around the exterior of a perforated liner and screen, with the pack preferably extending into the perforations in the unconsolidated formation. The gravel pack then presents a barrier to the migration of the sand while still allowing fluid to flow from the formation. In placing the gravel pack, the gravel is carried into the well and into the formation in the form of a slurry, with the carrier fluid or workover fluid being returned to the surface, leaving the gravel in the desired location.
Attempts have been made in the past to minimize the number of trips of the tool string into the well. Each trip of the tool string into a well takes an appreciable amount of time, and therefore incurs significant costs in terms of rig and crew time. As will be readily apparent, these costs are dramatically increased if the tool string is tripped to a great depth in a well.
Previous attempts to minimize trips into the borehole for gravel packing have only allowed the actual gravel packing operation to be performed in a single trip, but have not allowed the well to be placed on production at the end of that trip. Thus, with conventional so-called "one-trip" techniques, after a single trip into the borehole for gravel packing, the tubing and at least a portion of the tool string would have to be tripped out of the hole, and other equipment, such as a seal assembly or extension tripped into the hole to stab into the production packer to place the well on production. Examples of such prior art techniques are disclosed in U.S. Pat. No. 4,372,384, issued Jan. 10, 1983, and U.S. Pat. No. 4,566,538issued Jan. 28, 1986.
Accordingly, the present invention provides new methods and apparatus whereby a well may be gravel packed and placed on production with a single trip of the tool string and tubing into the wellbore. Additionally, the well may first be perforated on this same, single, trip into the wellbore.